Clarifier
Environmental Engineering · FE Reference Handbook section
Handbook notes for this section
Definitions and conditions exactly as the handbook states them.
- Typical Primary Clarifier Efficiency Percent Removal
- Design Criteria for Sedimentation Basins
- Overflow Rate Solids Loading Rate
- Type of Basin Average Peak Average Peak Time (ft)
Core formulas for this FE topic
Definitions, applicability, units, assumptions and worked examples for each relation.
Worked exam-style examples
The four ways this section is written on the real exam — thoughts first, then equations, then substitution.
tank volume required for a target detention time in a storage tank Given flow rate (Q) = 16,350 m^3/day; hydraulic detention time (theta) = 7.3000 day, determine the tank volume (V) in m^3.
Given
Find
tank volume (V), in m^3
Start with the thinking
- The governing relation printed in this handbook section is Tank Volume.
- Everything except V is given, so isolate V symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Tank volume for a treatment basin is the product of flow rate and required hydraulic detention time.
Figure 1 — schematic for Tank Volume — solve for tank volume — Clarifier
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for V:
Step 3 — List the givens: flow rate (Q) = 16,350 m^3/day, hydraulic detention time (theta) = 7.3000 day.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
V = 119355\ \text{m^3}Step 6 — Check: returning V = 119,355 m^3 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 238,710 — kept a factor of two that cancels in the correct rearrangement.
- 59,678 — dropped that same factor in the other direction.
- 131,291 — rounded an intermediate value before the final step.
Reference: FE Handbook — Tank Volume
tank volume sizing for an equalization basin Given hydraulic detention time (theta) = 5.1000 day; tank volume (V) = 149,316 m^3, determine the flow rate (Q) in m^3/day.
Given
Find
flow rate (Q), in m^3/day
Start with the thinking
- The governing relation printed in this handbook section is Tank Volume.
- Everything except Q is given, so isolate Q symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Tank volume for a treatment basin is the product of flow rate and required hydraulic detention time.
Figure 2 — schematic for Tank Volume — solve for flow rate — Clarifier (2)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for Q:
Step 3 — List the givens: hydraulic detention time (theta) = 5.1000 day, tank volume (V) = 149,316 m^3.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Q = 29278\ \text{m^3/day}Step 6 — Check: returning Q = 29,278 m^3/day to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 58,555 — kept a factor of two that cancels in the correct rearrangement.
- 14,639 — dropped that same factor in the other direction.
- 32,205 — rounded an intermediate value before the final step.
Reference: FE Handbook — Tank Volume
detention tank volume calculated from plant flow rate Given flow rate (Q) = 2,220 m^3/day; tank volume (V) = 218,303 m^3, determine the hydraulic detention time (theta) in day.
Given
Find
hydraulic detention time (theta), in day
Start with the thinking
- The governing relation printed in this handbook section is Tank Volume.
- Everything except theta is given, so isolate theta symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Tank volume for a treatment basin is the product of flow rate and required hydraulic detention time.
Figure 3 — schematic for Tank Volume — solve for hydraulic detention time — Clarifier (3)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for theta:
Step 3
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning theta = 98.3347 day to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 196.7 — kept a factor of two that cancels in the correct rearrangement.
- 49.1673 — dropped that same factor in the other direction.
- 108.2 — rounded an intermediate value before the final step.
Reference: FE Handbook — Tank Volume
tank volume required for a target detention time in a storage tank Given flow rate (Q) = 5,000 m^3/day; hydraulic detention time (theta) = 19.0000 day, determine the tank volume (V) in m^3.
Given
Find
tank volume (V), in m^3
Start with the thinking
- The governing relation printed in this handbook section is Tank Volume.
- Everything except V is given, so isolate V symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Tank volume for a treatment basin is the product of flow rate and required hydraulic detention time.
Figure 4 — schematic for Tank Volume — solve for tank volume (case 2) — Clarifier (4)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for V:
Step 3 — List the givens: flow rate (Q) = 5,000 m^3/day, hydraulic detention time (theta) = 19.0000 day.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
V = 95000\ \text{m^3}Step 6 — Check: returning V = 95,000 m^3 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 190,000 — kept a factor of two that cancels in the correct rearrangement.
- 47,500 — dropped that same factor in the other direction.
- 104,500 — rounded an intermediate value before the final step.
Reference: FE Handbook — Tank Volume
tank volume sizing for an equalization basin Given hydraulic detention time (theta) = 18.0000 day; tank volume (V) = 199,020 m^3, determine the flow rate (Q) in m^3/day.
Given
Find
flow rate (Q), in m^3/day
Start with the thinking
- The governing relation printed in this handbook section is Tank Volume.
- Everything except Q is given, so isolate Q symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Tank volume for a treatment basin is the product of flow rate and required hydraulic detention time.
Figure 5 — schematic for Tank Volume — solve for flow rate (case 2) — Clarifier (5)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for Q:
Step 3 — List the givens: hydraulic detention time (theta) = 18.0000 day, tank volume (V) = 199,020 m^3.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Q = 11057\ \text{m^3/day}Step 6 — Check: returning Q = 11,057 m^3/day to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 22,113 — kept a factor of two that cancels in the correct rearrangement.
- 5,528 — dropped that same factor in the other direction.
- 12,162 — rounded an intermediate value before the final step.
Reference: FE Handbook — Tank Volume
detention tank volume calculated from plant flow rate Given flow rate (Q) = 11,260 m^3/day; tank volume (V) = 21,977 m^3, determine the hydraulic detention time (theta) in day.
Given
Find
hydraulic detention time (theta), in day
Start with the thinking
- The governing relation printed in this handbook section is Tank Volume.
- Everything except theta is given, so isolate theta symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Tank volume for a treatment basin is the product of flow rate and required hydraulic detention time.
Figure 6 — schematic for Tank Volume — solve for hydraulic detention time (case 2) — Clarifier (6)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for theta:
Step 3
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning theta = 1.9518 day to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 3.9036 — kept a factor of two that cancels in the correct rearrangement.
- 0.9759 — dropped that same factor in the other direction.
- 2.1470 — rounded an intermediate value before the final step.
Reference: FE Handbook — Tank Volume
tank volume required for a target detention time in a storage tank Given flow rate (Q) = 15,100 m^3/day; hydraulic detention time (theta) = 9.0000 day, determine the tank volume (V) in m^3.
Given
Find
tank volume (V), in m^3
Start with the thinking
- The governing relation printed in this handbook section is Tank Volume.
- Everything except V is given, so isolate V symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Tank volume for a treatment basin is the product of flow rate and required hydraulic detention time.
Figure 7 — schematic for Tank Volume — solve for tank volume (case 3) — Clarifier (7)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for V:
Step 3 — List the givens: flow rate (Q) = 15,100 m^3/day, hydraulic detention time (theta) = 9.0000 day.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
V = 135900\ \text{m^3}Step 6 — Check: returning V = 135,900 m^3 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 271,800 — kept a factor of two that cancels in the correct rearrangement.
- 67,950 — dropped that same factor in the other direction.
- 149,490 — rounded an intermediate value before the final step.
Reference: FE Handbook — Tank Volume
tank volume sizing for an equalization basin Given hydraulic detention time (theta) = 0.9000 day; tank volume (V) = 79,559 m^3, determine the flow rate (Q) in m^3/day.
Given
Find
flow rate (Q), in m^3/day
Start with the thinking
- The governing relation printed in this handbook section is Tank Volume.
- Everything except Q is given, so isolate Q symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Tank volume for a treatment basin is the product of flow rate and required hydraulic detention time.
Figure 8 — schematic for Tank Volume — solve for flow rate (case 3) — Clarifier (8)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for Q:
Step 3 — List the givens: hydraulic detention time (theta) = 0.9000 day, tank volume (V) = 79,559 m^3.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Q = 88399\ \text{m^3/day}Step 6 — Check: returning Q = 88,399 m^3/day to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 176,798 — kept a factor of two that cancels in the correct rearrangement.
- 44,199 — dropped that same factor in the other direction.
- 97,239 — rounded an intermediate value before the final step.
Reference: FE Handbook — Tank Volume
detention tank volume calculated from plant flow rate Given flow rate (Q) = 3,320 m^3/day; tank volume (V) = 377,106 m^3, determine the hydraulic detention time (theta) in day.
Given
Find
hydraulic detention time (theta), in day
Start with the thinking
- The governing relation printed in this handbook section is Tank Volume.
- Everything except theta is given, so isolate theta symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Tank volume for a treatment basin is the product of flow rate and required hydraulic detention time.
Figure 9 — schematic for Tank Volume — solve for hydraulic detention time (case 3) — Clarifier (9)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for theta:
Step 3
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning theta = 113.6 day to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 227.2 — kept a factor of two that cancels in the correct rearrangement.
- 56.7931 — dropped that same factor in the other direction.
- 124.9 — rounded an intermediate value before the final step.
Reference: FE Handbook — Tank Volume
tank volume required for a target detention time in a storage tank Given flow rate (Q) = 6,100 m^3/day; hydraulic detention time (theta) = 7.1500 day, determine the tank volume (V) in m^3.
Given
Find
tank volume (V), in m^3
Start with the thinking
- The governing relation printed in this handbook section is Tank Volume.
- Everything except V is given, so isolate V symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Tank volume for a treatment basin is the product of flow rate and required hydraulic detention time.
Figure 10 — schematic for Tank Volume — solve for tank volume (case 4) — Clarifier (10)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for V:
Step 3 — List the givens: flow rate (Q) = 6,100 m^3/day, hydraulic detention time (theta) = 7.1500 day.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
V = 43615\ \text{m^3}Step 6 — Check: returning V = 43,615 m^3 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 87,230 — kept a factor of two that cancels in the correct rearrangement.
- 21,808 — dropped that same factor in the other direction.
- 47,977 — rounded an intermediate value before the final step.
Reference: FE Handbook — Tank Volume